Objective:
The terms Volume, Standard Volume, and Standard Liquid Volume can be confusing. OLI Systems uses all three terms in its calculations, but they each have distinct meanings.
This article aims to clarify the distinctions between Volume, Standard Volumes (i.e., "Volume, Std. Conditions"), and Standard Liquid Volumes reported in OLI software. These volume representations are available in the OLI output, as demonstrated in the Report examples below.
Standard Liquid Volume and Standard Volume, as reported in OLI Studio
Volumes
OLI calculates a system's volume based on its internal thermodynamic techniques. The system's volume is at a given temperature, pressure, and composition. It is often called the "Real" or "Actual" volume of the system. OLI also calculates the volume of each phase predicted.
Standard Volume
The Standard Volume, which is calculated at standard conditions using the compositions of each phase from the previous flash calculation, is the volume at standard conditions.
Vapor:
Total moles and composition: Retrieved from previously equilibrated compositions at system temperature and pressure.
- Standard temperature: 15.556oC (default)
- Standard pressure: 1.0023 atm (default)
- Volume is recalculated at the standard temperature and pressure.
The standard temperature and pressure can be set in the program options.
Aqueous or Liquid-1:
Total moles and composition: Retrieved from previously equilibrated compositions at system temperature and pressure.
- Standard temperature: 25.0oC (default)
- Standard pressure: 1.0 atm (default)
- Volume is recalculated at the standard temperature and pressure.
The standard temperature and pressure can be set in the program options.
Organic or Liquid-2:
Total moles and composition: Retrieved from previously equilibrated compositions at system temperature and pressure.
- Standard temperature: 15.0oC (default)
- Standard pressure: 1.0 atm (default)
- Volume is recalculated at the standard temperature and pressure.
The standard temperature and pressure can be set in the program options.
Standard Liquid Volume
Unlike Standard Volume, the Standard Liquid Volume is calculated based on true species. This property is computed for all the phases present in the system.
Example: Back-Calculate the Liq-1 Standard Liquid Volume
We will demonstrate how Standard Liquid Volume can be manually back-calculated for the Liquid-1 phase to reproduce the results generated by OLI Studio V12.0.0.11.
The stream input properties are as follows:
- H2O: 55.5082 moles
- NaCl: 1 mole
- Temperature: 25°C
- Pressure: 1 atm
- Thermodynamic Framework: MSE
The values for the Standard Liquid Volume of different Material Balance Groups (MBG) can be found in the OLI Databook. In the MSEPUB database, navigate to the Material Codes section. Here, each Material Code entry includes a characteristic Liquid Volume entry. These values are listed below.
| MBG name | Standard liquid volume of MBG, VOLU (m3) |
|---|---|
| H(+1) | 1.4120E-05 |
| Na(+1) | 1.81624E-05 |
| O(-2) | -1.01728E-05 |
| Cl(-1) | 1.7172E-05 |
After running the OLI Studio Isothermal Single Point calculation, the Liquid-1 true species composition is as follows:
| True species (Name) | Composition (COMP), mole |
|---|---|
| H2O | 55.5082 |
| Cl-1 | 1 |
| Na+1 | 1 |
| H3O+1 | 1.33E-07 |
| OH-1 | 1.33E-07 |
| NaOH | 5.30E-14 |
| HCl | 2.07E-15 |
The Standard Liquid Volume of this phase can be calculated by considering the MBG group contributions of each true species, as outlined below.
| MBG Name | Contribution | Contribution Value |
|---|---|---|
| H(+1) | 1.4120E-05*(55.5082*2 + 1.33E-07*3 + 1.33E-07*1 + 5.30E-14*1 + 2.07E-15*1) | 1.57E-03 |
| Na(+1) | 1.8162E-05*(1*1 + 5.30E-14*1) | 1.82E-05 |
| O(-2) | -1.01725E-05*(55.5082*1 + 1.33E-07*1 + 1.33E-07*1 + 5.30E-14*1) | -5.65E-04 |
| Cl(-1) | 1.7172E-05*(1*1 + 2.07E-15*1) | 1.72E-05 |
| Volume (m3) | 0.00103827 | |
| Volume (L) | 1.03827 |
This matches the value generated by the OLI software.